Thorndale is a census-designated place (CDP) in Chester County, Pennsylvania, United States. The population was 3,407 at the 2010 census. Thorndale is the commercial and administrative center of Caln Township. The community's main street is Business U.S. Route 30. Many of the old houses that were Thorndale have fallen into disrepair and have been torn down and replaced with new business from the late 1990s to present.